Immunoassays have been used in recent years to detect the presence of infectious diseases. In order for the assay to be useful, it must detect a particular organism with a high degree of reliability. In most cases, this requires the isolation and reaction of antigens peculiar to the organism with corresponding antibodies. For the test to be commercially successful, it also needs to be relatively inexpensive, simple to use and rapid.
One such organism which can be detected by immunoassay is Chlamydia trachomatis (herein C. trachomatis) which is one of two microbial species of the genus Chlamydiaceae, order Chlamydiales. There are 15 or more strains of this species which are the causes of a number of human ocular and genital diseases including trachoma, inclusion conjunctivitis, lymphogranuloma venereum, nongonococcal urethritis and proctitis. Infection from C. trachomatis is pervasive in the general population so that it is believed that there are millions of cases each year of nongonococcal urethritis alone.
Gonorrhea is a disease usually transmitted by sexual contact caused by a bacterium of the Neisseria genus, especially N. gonorrhoeae. The disease has plagued mankind for thousands of years, and although antibiotics have helped control its spread, it still persists in epidemic proportions in many parts of the world. The importance of detection and treatment of this organism is well recognized. N. meningitidis and N. lactamica are also species of considerable medical and diagnostic interest.
Because of the widespread nature of these diseases, there is considerable interest in having a rapid, simple and reliable test for detection of chlamydial and gonococcal organisms. Considerable research has been carried out to find useful ways to extract detectable antigen from chlamydial organisms. See for example, U.S. Pat. No. 4,427,782 (issued Jan. 24, 1984 to Caldwell et al) and E.P. Publication 193,431 (Caldwell et al).
Assays for C. trachomatis and N. gonorrhoeae carried out using a solid support are described in U.S. Pat. No. 4,497,899 and 4,497,900, respectively (both issued Feb. 5, 1985 to Armstrong et al and Abram et al, respectively). Extraction is carried out using various nonionic or anionic surfactants. In addition, the '899 patent mentions that it is preferred to include a reducing agent (such as dithiothreitol, 2-mercaptoethanol or N-acetylcysteine) in the chlamydial extraction medium.
Dithiothreitol is used in the extraction procedures described in U.S. Pat. No. 4,427,782 and E.P. Publication 193,431 (both noted above).
While dithiothreitol or other sulfhydryl-containing reducing agents are known to be useful in chlamydial antigen extraction to solubilize extraneous proteins, such agents are generally unstable, and rapidly lose their activity unless used right away. Therefore, it would be desirable to have extraction compositions and diagnostic test kits which can be stored for a lengthy period of time. Without this stability, such materials lack significant commercial interest.